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A reduction in the amount of nitrogen oxides being discharged into the atmosphere in combustion gases emitted from industrial plants has become an important goal.
The most efficient secondary technique for removing such nitrogen oxides from the burning of fuels, such as coal, oil and natural gas, municipal and hazardous waste, is their conversion into inert nitrogen gas by reaction with a reducing reagent using the Selective Catalytic Reduction technology (SCR).
Reduction efficiencies of 90% and more can be achieved with this process, which mainly consists in the injection of a reducing agent upstream one or more catalyst layers, where the following reactions take place:
Catalysts may be produced in different configurations. For SCR DeNOx plants, however, honeycomb and plate type catalysts are mainly used. Honeycomb structures are obtained by extruding a mass of paste composed of catalytic material, while plate catalysts consist of a stainless steel net on which the catalytic material is pressed.
Oxides of vanadium, titanium and tungsten (V2O5, TiO2, and WO3) are widely used for ceramic monolith and composite SCR catalysts. Titanium oxides typically constitutes the support while vanadium is the active principle.
Operating temperature ranges from 180 °C up to 500 °C, depending on several parameters like type of fuel, flue gas composition and, configuration of upstream flue gas treatment.
The catalyst is installed inside a Reactor that can be positioned in different alternative places along the flue gas treatment line. Two configurations are the most commonly used: the High Dust System (upstream Flue Gas Treatment) and the Tail End System (which operates with cleaned gas). The best solution is obtained taking into account process parameters, layout considerations and economical evaluations. 
With more than 11.000 MW of successfully realised installations, Termokimik is a leading supplier of SCR systems to reduce emissions of Nitrogen Oxides.
The main advantages of Termokimik SCR systems are:
Optimum Catalyst Design
Termokimik's extensive experience and the close collaboration with primary catalyst manufacturers allows to select the appropriate design for a given application, thus optimising process performances and lifetime.
Low Installation Downtime
Most of Termokimik's references are retrofits of existing plants. The huge experience accumulated over the last ten years allows to conceive the installation in order to minimise the boiler downtime.
Integrated Process Approach
The presence of an SCR system introduces some modifications in the Flue Gas composition and properties (additional pressure drop, SO2/SO3 conversion, NH3 slip) which may have an impact on the downstream equipment. As a supplier of almost every kind o f Flue Gas Treatment equipment, Termokimik can design an SCR system that can be properly integrated along the flue gas stream and, if needed, carry out modifications on the equipment which may not be able to operate under the new conditions.
Optimised NH 3 /NOx distribution
NH 3 /NOx ratio, velocity distribution and temperature distribution are key parameters to meet the performance guarantees. TKC always uses physical and/or computer flow models to design flow straightening devices and ammonia injection grids and to estimate gas flow and temperature distribution. |
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